Bar screens are used for screening comparatively large solids from flowing fluids, in particular liquids and free-flowing bulk material and similar, in the most varied fields of engineering. Examples of bar screens of this type are disclosed in DE 603 07 789 T2, DE 41 26 240 C1, and EP 0 265 421 A2.
It is a common feature of the known bar screens that the screen effect is achieved by screen bars which are disposed so as to be mutually parallel and which by way of one end thereof are held on a support unit and by way of the other end are freely suspended in the flow or conveying path of the product to be screened. The gap width interdisposed between the screen bars here determines the minimum size above which the particles impacting the screen are separated or up to which particle size they may pass through the screen. Since the ends of the screen bars run out freely, the risk of blockage by the screened product is low. The screen bars here are typically disposed in one plane. Conveying of the screened product via the bar screen here may also be performed by the screen bars toward the free end thereof being downwardly inclined. Linear conveying of the screened product is then typically supported by an up-and-down movement of the free end of the screen bars, which is caused by an eccentric.
Irrespective of the field of application, screen bars are subjected to high dynamic load during use, since the respective particles to be filtered in each case have a comparatively large mass and thus impact the bars with a high kinetic energy. At the same time, screen bars which are employed for example in comminution machines, such as hammer crushers or shredders, are exposed to enormous load by abrasive wear.
The effort associated with the replacement of screen bars, which is required at short intervals, is significant. As a consequence there is the demand for screen bars to be immune to abrasive wear, on the one hand, and to have sufficiently good spring characteristics, on the other hand, so as to be able to also absorb hard shocks which arise at high frequency, without the risk of a material failure.
In order to meet this profile of requirements, freely suspended screen bars of the type discussed here in practice are typically made from spring-steel varieties or other high-strength steel materials which permit sufficient elastic deformation.
As is explained in DE 41 26 240 C1, the wear resistance of screen bars which are manufactured from such steel varieties and which in the respective prior art are destined for vegetable oil presses may be further increased in that the screen bars are provided with a wear-resistant coating. The coating is to consist of a composite material having 60-80% by volume of a hard material and 20-40% by volume of a solder alloy. Preferably, tungsten carbide and/or chromium carbide is to be used as a hard material and nickel-based solders, for example a Ni—Cr—B—Si alloy, are to be used as a solder alloy.
The advantage of a composite material coating of this type is said to lie in that said composite material coating adheres particularly well to the respective steel substrate and offers good protection against wear. However, a manufacturing method which is comparatively complex and which moreover may cause thermally-induced distortion of the screen bars which have to be individually coated is required to this end.